In recent years, a magnetic head for perpendicular magnetic recording has been suggested to realize high recording density, large capacity or miniaturization of a magnetic disk device as a disk device. In this type of magnetic head, a recording head includes a main magnetic pole which produces a perpendicular magnetic field, a write shield magnetic pole provided on the trailing side of the main magnetic pole across an intervening write gap, and a coil for supplying a magnetic flux to the main magnetic pole. Further, the following high-frequency (microwave) assisted head has been suggested. In the high-frequency assisted head, a high-frequency (microwave) oscillator such as a spin-torque oscillator is provided in the write gap between the write shield magnetic pole and the main magnetic pole. Current is supplied to the spin-torque oscillator through the main magnetic pole and the write shield magnetic pole.
In the high-frequency-assisted head, the spin injection layer and the oscillation layer of the high-frequency oscillator are allocated in the write gap. In the high-frequency-assisted head having this structure, the magnetization near the surface of the write shield or the main magnetic pole facing the surface of the oscillation layer vibrates so as to be synchronized with the rotation of magnetization of the oscillation layer. Thus, a spin wave is generated. This spin wave may disturb the rotation of magnetization of the high-frequency oscillator and inhibit the assist effect.